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  • Prochazka, David  (17)
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  • 1
    Language: English
    In: Analytical chemistry, 16 October 2018, Vol.90(20), pp.11820-11826
    Description: Nanoparticles (NPs) applied to the surface of some solids can increase signals in inductively coupled plasma mass spectrometry (ICPMS). Drops containing 20 and/or 40 nm nanoparticles of Ag and/or Au were deposited on metallic and ceramic/glass samples, and after being dried, both the samples treated with NPs and plain targets were ablated by one pulse per spot. The laser ablation ICPMS (LA-ICPMS) signals were enhanced for metallic samples modified with NPs in comparison to signals produced at the plain, untreated surface. Maps of LA-ICPMS signals recorded for several laser fluences show that the NP-induced signal enhancement exceeds even 2 orders of magnitude for metallic samples. No enhancement was achieved for nonconductive samples. This enhancement is limited to the peripheral annular region of the dried droplet area where NPs are concentrated due to the "coffee stain" effect. Ablation crater profilometric inspection revealed a more uniform material rearrangement over the NP-treated surface compared with the ablated plain target. However, besides a smoother crater bottom, no other evidence of an NP-enhancing effect was noticed, although an increased ablation rate was anticipated. Limits of detection dropped by 1 order of magnitude for the minor elements in the presence of NPs. Observed phenomena depend only on the NP surface concentration but not on the material or size of the NPs. An electron microprobe study of the collected ablation aerosol has shown that aerosol particles consisting of target material are aggregated around the NPs. The hypothesis is that such aggregates exhibit better transport/vaporization efficiency, thus enhancing signals for metallic samples. A detailed study of the suggested mechanism will be continued in ongoing work.
    Keywords: Photoablation ; Nanoparticles ; Earthquake-Intensity ; Droplets ; Solids ; Detection-Limit ; Lasers ; Crater ; Icp-MS:Inductively-Coupled-Plasma-Mass-Spectrometry ; Aerosols ; Electron-Microprobes ; Laserablation ; Nanopartikel ; Erdbebenmagnitude ; Tröpfchen ; Festkörper ; Nachweisgrenze ; Laser ; Krater ; Massenspektrometrie Mit Induktiv Gekoppeltem Plasma ; Aerosol ; Elektronenmikrosonde ; Engineering ; Chemistry;
    ISSN: 00032700
    E-ISSN: 1520-6882
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  • 2
    Language: English
    In: Review of Scientific Instruments, April 2016, Vol.87(4)
    Description: A complex optimization of geometrical and temporal parameters of a jet system (developed in Laser-induced breakdown spectroscopy (LIBS) laboratory of Brno University of Technology) for direct elemental analysis of samples in a liquid state of matter using LIBS was carried out. First, the peristaltic pump was synchronized with the flashlamp of the ablation laser, which reduced variation of the ablated sample amount. Also, the fluctuation of the laser ray angle incident on the jet surface was diminished. Such synchronization reduced signal standard deviations and thus increased repeatability of the measurements. Then, laser energy and distance of the focusing lens from the sample were optimized. The gate delay time and the gate width were optimized for single pulse (SP) experiments; the gate delay time and the inter-pulse delay were optimized for the use of double pulse (DP) variant. Results were assessed according to the highest signal to noise ratios and the lowest relative standard deviations of the signal. The sensitivity of the single pulse and the double pulse LIBS for the detection of heavy metals traces, copper (Cu i at 324.754 nm) and lead (Pb i at 405.781 nm), in aqueous solution of copper ( ii ) sulfate and lead ( ii ) acetate, was estimated in terms of limits of detection (LODs). As a result, sensitivity improvement of DP LIBS system was observed, the LOD of Cu obtained with DP was calculated 40% lower than LOD gained from SP technique.
    Keywords: Articles
    ISSN: 0034-6748
    E-ISSN: 1089-7623
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  • 3
    Language: English
    In: Spectrochimica Acta Part B: Atomic Spectroscopy, October 2018, Vol.148, pp.65-82
    Description: An implementation of a fast, robust, and effective algorithm is inevitable in modern multivariate data analysis (MVDA). The principal component analysis (PCA) algorithm is becoming popular not only in the spectroscopic community because it complies with the qualities mentioned above. PCA is, therefore, often used for the processing of detected multivariate signal (characteristic spectra). Over the past decade, PCA has been adopted by the Laser-Induced Breakdown Spectroscopy (LIBS) community and the number of scientific articles referring to PCA steadily increases. The interest in PCA is not caused only by the basic need to obtain a fast data visualization on a lower dimensional scale and to inspect the most prominent variables. Most recently, PCA has also been applied to yield unconventional data analyses, processing of large scale LIBS maps. However, a rapid development of LIBS-related instrumentation and applications has led to some non-uniform methodologies in the implementation and utilization of MVDA, including PCA. Thus, in this work, we critically assess and elaborate on the approaches to utilize PCA in LIBS data processing. The aim of this article is also to derive some implications and to suggest advice in data preprocessing, visualization, dimensionality reduction, model building, classification, quantification and non-conventional multivariate mapping. This review reflects also other MVDA algorithms than PCA and consequently, presented conclusions and recommendations can be generalized.
    Keywords: Chemistry ; Physics
    ISSN: 0584-8547
    E-ISSN: 1873-3565
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  • 4
    Language: English
    In: Spectrochimica Acta Part B: Atomic Spectroscopy, 01 December 2016, Vol.126, pp.6-10
    Description: The purpose of this work is to provide detailed study of statistical behavior of different types of analytical signals in typical of Laser-Induced Breakdown Spectroscopy (LIBS) measurements. The main goal of this work is to justify usage of arithmetic mean and standard deviation as statistical estimates of expected value of selected analytical signal. In contrary to the general assumption that LIBS data show Gaussian distribution, this paper deals with the hypothesis that the data rather demonstrate Generalized Extreme Value Distribution. The study is realized on 10 selected lines measured on NIST glass standard. In order to cover wide range of possible applications three different spectra internal standardization techniques and their influence on distribution were studied. Finally, assuming that the data comes from a single distribution and the central limit theorem is valid, the influence of accumulations on the line distribution is examined and discussed. Statistical tools used and described in this paper can be utilized by other researchers to confirm their hypotheses and verify utilization of Gaussian distribution or even novel data processing methods.
    Keywords: Laser-Induced Breakdown Spectroscopy ; Generalized Extreme Value Distribution, Shot-to-Shot Statistics ; Chemistry ; Physics
    ISSN: 0584-8547
    E-ISSN: 1873-3565
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  • 5
    Language: English
    In: Spectrochimica Acta Part B: Atomic Spectroscopy, 01 October 2016, Vol.124, pp.116-123
    Description: The objective of this work was to assess a part of echelle Laser-Induced Plasma spectra (ranging from 200 to 1000 nm) that could be most effectively employed for rocks classification. Therefore, a 60 nm wide spectral window mask was iteratively moved over the broadband echelle spectra. Each created narrow artificial spectral windows (60 nm) was used for the classification of rock samples using various Multivariate Data Analysis (MVDA) algorithms, reaching more than 99% of the overall accuracy in certain cases. Afterwards, the Czerny-Turner spectrometer (having higher sensitivity compared to the echelle spectrometer) was aligned to the selected and the most effective spectral regions and rocks samples were re-measured. Consequently the MVDA analyses were utilized again, providing also satisfying classification results yielding more than 99% of the overall accuracy. Measurements of 28 sedimentary ores (certified reference materials) were done utilizing commercially available X-Trace device (AtomTrace), where spectrometers in both configurations (echelle and Czerny-Turner) were exploited.
    Keywords: Laser-Induced Breakdown Spectroscopy ; Multivariate Classification ; Echelle Spectrometer ; Czerny-Turner Spectrometer ; Chemistry ; Physics
    ISSN: 0584-8547
    E-ISSN: 1873-3565
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  • 6
    Language: English
    In: Spectrochimica Acta Part B: Atomic Spectroscopy, 01 May 2017, Vol.131, pp.66-73
    Description: This paper presents a novel approach for processing the spectral information obtained from high-resolution elemental mapping performed by means of Laser-Induced Breakdown Spectroscopy. The proposed methodology is aimed at the description of possible elemental associations within a heterogeneous sample. High-resolution elemental mapping provides a large number of measurements. Moreover, typical laser-induced plasma spectrum consists of several thousands of spectral variables. Analysis of heterogeneous samples, where valuable information is hidden in a limited fraction of sample mass, requires special treatment. The sample under study is a sandstone-hosted uranium ore that shows irregular distribution of ore elements such as zirconium, titanium, uranium and niobium. Presented processing methodology shows the way to reduce the dimensionality of data and retain the spectral information by utilizing self-organizing maps (SOM). The spectral information from SOM is processed further to detect either simultaneous or isolated presence of elements. Conclusions suggested by SOM are in good agreement with geological studies of mineralization phases performed at the deposit. Even deeper investigation of the SOM results enables discrimination of interesting measurements and reveals new possibilities in the visualization of chemical mapping information. Suggested approach improves the description of elemental associations in mineral phases, which is crucial for the mining industry.
    Keywords: Laser-Induced Breakdown Spectroscopy ; Uranium Ore ; Elements Distribution ; Self-Organizing Maps ; Chemistry ; Physics
    ISSN: 0584-8547
    E-ISSN: 1873-3565
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  • 7
    Language: English
    In: Spectrochimica Acta Part B: Atomic Spectroscopy, 01 September 2016, Vol.123, pp.114-120
    Description: In this manuscript we highlight the necessity of outlier filtering prior the multivariate classification in Laser-Induced Breakdown Spectroscopy (LIBS) analyses. For the purpose of classification we chose to analyse BAM steel standards that possess similar composition of major and trace elements. To assess the improvement in figures of merit we compared the performance of three outlier filtering approaches (based on Principal Component Analysis, linear correlation and total spectral intensity) already separately discussed in the LIBS literature. The truncated data set was classified using Soft Independent Modelling of Class Analogies (SIMCA). Yielded results showed significant improvement in the performance of multivariate classification coupled to filtered data. The best performance was observed for the total spectral intensity filtering approach gaining the analytical figures of merit (overall accuracy, sensitivity, and specificity) over 98%. It is noteworthy that the results showed relatively low sensitivity and high specificity of the SIMCA algorithm regardless of the presence of outliers in the data sets. Moreover, it was shown that the variance in the data topology of training and testing data sets has a great impact on the consequent data classification.
    Keywords: Laser-Induced Breakdown Spectroscopy, Libs ; Outlier Filtering ; Principal Component Analysis, PCA ; Linear Correlation ; Total Spectral Intensity ; Soft Independent Modelling of Class Analogies, Simca ; Chemistry ; Physics
    ISSN: 0584-8547
    E-ISSN: 1873-3565
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  • 8
    Language: English
    In: Spectrochimica Acta Part B: Atomic Spectroscopy, July 2012, Vol.73, pp.1-6
    Description: The goal of this paper is to compare two selected statistical techniques used for identification of archeological materials merely on the base of their spectra obtained by stand-off laser-induced breakdown spectroscopy (stand-off LIBS). Data processing using linear discriminant analysis (LDA) and artificial neural networks (ANN) were applied on spectra of 18 different samples, some of them archeological and some recent, containing 7 types of material (i.e. shells, mortar, bricks, soil pellets, ceramic, teeth and bones). As the input data PCA scores were taken. The intended aim of this work is to create a database for simple and fast identification of archeological or paleontological materials . This approach can speed up and simplify the sampling process during archeological excavations that nowadays tend to be quite damaging and time-consuming. ► We use statistical techniques for identification of archeological materials. ► Input data for LDA and ANN are PC scores counted from stand-off LIBS spectra. ► The method used for identification of archeological materials provides good results. ► After recording more spectra we can get useful tool for rapid analysis .
    Keywords: Stand‐Off Libs ; PCA ; Lda ; Ann ; Biomineral ; Geomaterial ; Archeology ; Chemistry ; Physics
    ISSN: 0584-8547
    E-ISSN: 1873-3565
    Source: ScienceDirect Journals (Elsevier)
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  • 9
    Language: English
    In: Sci Rep, 2017, Vol.7(1), pp.3160-3160
    Description: In this work, we proposed a new data acquisition approach that significantly improves the repetition rates of Laser-Induced Breakdown Spectroscopy (LIBS) experiments, where high-end echelle spectrometers and intensified detectors are commonly used. The moderate repetition rates of recent LIBS systems are caused by the utilization of intensified detectors and their slow full frame (i.e. echellogram) readout speeds with consequent necessity for echellogram-to-1D spectrum conversion (intensity vs. wavelength). Therefore, we investigated a new methodology where only the most effective pixels of the echellogram were selected and directly used in the LIBS experiments. Such data processing resulted in significant variable down-selection (more than four orders of magnitude). Samples of 50 sedimentary ores samples (distributed in 13 ore types) were analyzed by LIBS system and then classified by linear and non-linear Multivariate Data Analysis algorithms. The utilization of selected pixels from an echellogram yielded increased classification accuracy compared to the utilization of common 1D spectra.
    Keywords: Biology;
    ISSN: 2045-2322
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  • 10
    Language: English
    In: Spectrochimica Acta Part B: Atomic Spectroscopy, April 2018, Vol.142, pp.8-13
    Description: A LIBS equipment operating at 532 nm was optimized and used for sulfur determination in concrete samples. The influence of He atmosphere in a gas-tight chamber (1000–200 mbar) on S I 921.29 nm line sensitivity, signal-to-background and signal-to-noise ratio was studied at gate delays 100–2000 ns. Wide range of gate delays from 500 to about 1000 ns and pressures from several hundreds of mbar to the atmospheric pressure can be used for the desired detection of sulfur. The LIBS quantification was done using a simple calibration method. A synthetic limestone enriched by defined amounts of sodium sulfate was newly employed for direct quantification of S in concrete. This powder material was pressed into pellets and ablated with the LIBS system. The average content of sulfur as SO in the samples was 0.41–0.70 wt% by LIBS and 0.43–0.61 wt% by a reference standard procedure employing gravimetry and Inductively Coupled Plasma Triple Quad Mass Spectrometry (ICP-QQQMS). The uncertainty of the yielded LIBS results covers also the dispersion of the points in the calibration line and ranges from 16 to 28% at the probability level of 95%. The uncertainty of the ICP-QQQMS results was almost 10%. No correction on different signal response on the limestone and on the concrete was necessary.
    Keywords: Sulfur ; Concrete ; Limestone ; Standard ; Laser ; Induced ; Breakdown ; Spectroscopy ; Inductively Coupled ; Plasma ; Mass Spectrometry ; Triple ; Quadrupole ; Chemistry ; Physics
    ISSN: 0584-8547
    E-ISSN: 1873-3565
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